Proton arc reduces range uncertainty effects and improves conformality compared with photon volumetric modulated arc therapy in stereotactic body radiation therapy for non-small cell lung cancer.

To describe, in a setting of non-small cell lung cancer (NSCLC), the theoretical dosimetric advantages of proton arc stereotactic body radiation therapy (SBRT) in which the beam penumbra of a rotating beam is used to reduce the impact of range uncertainties. Thirteen patients with early-stage NSCLC treated with proton SBRT underwent repeat planning with photon volumetric modulated arc therapy (Photon-VMAT) and an in-house-developed arc planning approach for both proton passive scattering (Passive-Arc) and intensity modulated proton therapy (IMPT-Arc). An arc was mimicked with a series of beams placed at 10° increments. Tumor and organ at risk doses were compared in the context of high- and low-dose regions, represented by volumes receiving >50% and <50% of the prescription dose, respectively. In the high-dose region, conformality index values are 2.56, 1.91, 1.31, and 1.74, and homogeneity index values are 1.29, 1.22, 1.52, and 1.18, respectively, for 3 proton passive scattered beams, Passive-Arc, IMPT-Arc, and Photon-VMAT. Therefore, proton arc leads to a 30% reduction in the 95% isodose line volume to 3-beam proton plan, sparing surrounding organs, such as lung and chest wall. For chest wall, V30 is reduced from 21 cm(3) (3 proton beams) to 11.5 cm(3), 12.9 cm(3), and 8.63 cm(3) (P=.005) for Passive-Arc, IMPT-Arc, and Photon-VMAT, respectively. In the low-dose region, the mean lung dose and V20 of the ipsilateral lung are 5.01 Gy(relative biological effectiveness [RBE]), 4.38 Gy(RBE), 4.91 Gy(RBE), and 5.99 Gy(RBE) and 9.5%, 7.5%, 9.0%, and 10.0%, respectively, for 3-beam, Passive-Arc, IMPT-Arc, and Photon-VMAT, respectively. Stereotactic body radiation therapy with proton arc and Photon-VMAT generate significantly more conformal high-dose volumes than standard proton SBRT, without loss of coverage of the tumor and with significant sparing of nearby organs, such as chest wall. In addition, both proton arc approaches spare the healthy lung from low-dose radiation relative to photon VMAT. Our data suggest that IMPT-Arc should be developed for clinical use.

Seco J ，Gu G ，Marcelos T ，Kooy H ，Willers H ... -  《-》

Treatment of non-small cell lung cancer patients with proton beam-based stereotactic body radiotherapy: dosimetric comparison with photon plans highlights importance of range uncertainty.

Proton beam radiotherapy has been proposed for use in stereotactic body radiotherapy (SBRT) for early-stage non-small-cell lung cancer. In the present study, we sought to analyze how the range uncertainties for protons might affect its therapeutic utility for SBRT. Ten patients with early-stage non-small-cell lung cancer received SBRT with two to three proton beams. The patients underwent repeat planning for photon SBRT, and the dose distributions to the normal and tumor tissues were compared with the proton plans. The dosimetric comparisons were performed within an operational definition of high- and low-dose regions representing volumes receiving >50% and <50% of the prescription dose, respectively. In high-dose regions, the average volume receiving ≥95% of the prescription dose was larger for proton than for photon SBRT (i.e., 46.5 cm(3) vs. 33.5 cm(3); p = .009, respectively). The corresponding conformity indexes were 2.46 and 1.56. For tumors in close proximity to the chest wall, the chest wall volume receiving ≥30 Gy was 7 cm(3) larger for protons than for photons (p = .06). In low-dose regions, the lung volume receiving ≥5 Gy and maximum esophagus dose were smaller for protons than for photons (p = .019 and p < .001, respectively). Protons generate larger high-dose regions than photons because of range uncertainties. This can result in nearby healthy organs (e.g., chest wall) receiving close to the prescription dose, at least when two to three beams are used, such as in our study. Therefore, future research should explore the benefit of using more than three beams to reduce the dose to nearby organs. Additionally, clinical subgroups should be identified that will benefit from proton SBRT.

Seco J ，Panahandeh HR ，Westover K ，Adams J ，Willers H ... -  《-》

Dosimetric considerations to determine the optimal technique for localized prostate cancer among external photon, proton, or carbon-ion therapy and high-dose-rate or low-dose-rate brachytherapy.

To assess the dosimetric differences among volumetric modulated arc therapy (VMAT), scanned proton therapy (intensity-modulated proton therapy, IMPT), scanned carbon-ion therapy (intensity-modulated carbon-ion therapy, IMIT), and low-dose-rate (LDR) and high-dose-rate (HDR) brachytherapy (BT) treatment of localized prostate cancer. Ten patients were considered for this planning study. For external beam radiation therapy (EBRT), planning target volume was created by adding a margin of 5 mm (lateral/anterior-posterior) and 8 mm (superior-inferior) to the clinical target volume. Bladder wall (BW), rectal wall (RW), femoral heads, urethra, and pelvic tissue were considered as organs at risk. For VMAT and IMPT, 78 Gy(relative biological effectiveness, RBE)/2 Gy were prescribed. The IMIT was based on 66 Gy(RBE)/20 fractions. The clinical target volume planning aims for HDR-BT ((192)Ir) and LDR-BT ((125)I) were D(90%) ≥34 Gy in 8.5 Gy per fraction and D(90%) ≥145 Gy. Both physical and RBE-weighted dose distributions for protons and carbon-ions were converted to dose distributions based on 2-Gy(IsoE) fractions. From these dose distributions various dose and dose-volume parameters were extracted. Rectal wall exposure 30-70 Gy(IsoE) was reduced for IMIT, LDR-BT, and HDR-BT when compared with VMAT and IMPT. The high-dose region of the BW dose-volume histogram above 50 Gy(IsoE) of IMPT resembled the VMAT shape, whereas all other techniques showed a significantly lower high-dose region. For all 3 EBRT techniques similar urethra D(mean) around 74 Gy(IsoE) were obtained. The LDR-BT results were approximately 30 Gy(IsoE) higher, HDR-BT 10 Gy(IsoE) lower. Normal tissue and femoral head sparing was best with BT. Despite the different EBRT prescription and fractionation schemes, the high-dose regions of BW and RW expressed in Gy(IsoE) were on the same order of magnitude. Brachytherapy techniques were clearly superior in terms of BW, RW, and normal tissue sparing, with lowest values for HDR-BT.

Georg D ，Hopfgartner J ，Gòra J ，Kuess P ，Kragl G ，Berger D ，Hegazy N ，Goldner G ，Georg P ... -  《-》

Circumferential or sectored beam arrangements for stereotactic body radiation therapy (SBRT) of primary lung tumors: effect on target and normal-structure dose-volume metrics.

To compare 2 beam arrangements, sectored (beam entry over ipsilateral hemithorax) vs circumferential (beam entry over both ipsilateral and contralateral lungs), for static-gantry intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) delivery techniques with respect to target and organs-at-risk (OAR) dose-volume metrics, as well as treatment delivery efficiency. Data from 60 consecutive patients treated using stereotactic body radiation therapy (SBRT) for primary non-small-cell lung cancer (NSCLC) formed the basis of this study. Four treatment plans were generated per data set: IMRT/VMAT plans using sectored (-s) and circumferential (-c) configurations. The prescribed dose (PD) was 60Gy in 5 fractions to 95% of the planning target volume (PTV) (maximum PTV dose ~ 150% PD) for a 6-MV photon beam. Plan conformality, R50 (ratio of volume circumscribed by the 50% isodose line and the PTV), and D2cm (Dmax at a distance ≥2cm beyond the PTV) were evaluated. For lungs, mean doses (mean lung dose [MLD]) and percent V30/V20/V10/V5Gy were assessed. Spinal cord and esophagus Dmax and D5/D50 were computed. Chest wall (CW) Dmax and absolute V30/V20/V10/V5Gy were reported. Sectored SBRT planning resulted in significant decrease in contralateral MLD and V10/V5Gy, as well as contralateral CW Dmax and V10/V5Gy (all p < 0.001). Nominal reductions of Dmax and D5/D50 for the spinal cord with sectored planning did not reach statistical significance for static-gantry IMRT, although VMAT metrics did show a statistically significant decrease (all p < 0.001). The respective measures for esophageal doses were significantly lower with sectored planning (p < 0.001). Despite comparable dose conformality, irrespective of planning configuration, R50 significantly improved with IMRT-s/VMAT-c (p < 0.001/p = 0.008), whereas D2cm significantly improved with VMAT-c (p < 0.001). Plan delivery efficiency improved with sectored technique (p < 0.001); mean monitor unit (MU)/cGy of PD decreased from 5.8 ± 1.9 vs 5.3 ± 1.7 (IMRT) and 2.7 ± 0.4 vs 2.4 ± 0.3 (VMAT). The sectored configuration achieves unambiguous dosimetric advantages over circumferential arrangement in terms of esophageal, contralateral CW, and contralateral lung sparing, in addition to being more efficient at delivery.

Rosenberg MW ，Kato CM ，Carson KM ，Matsunaga NM ，Arao RF ，Doss EJ ，McCracken CL ，Meng LZ ，Chen Y ，Laub WU ，Fuss M ，Tanyi JA ... -  《-》

Stereotactic body radiotherapy: volumetric modulated arc therapy versus 3D non-coplanar conformal radiotherapy for the treatment of early stage lung cancer.

Herbert C ，Kwa W ，Nakano S ，James K ，Moiseenko V ，Wu J ，Schellenberg D ，Liu M ... -  《-》